Calutron



June 28, 1955 P. HUNTER 2,712,079

cALUTRoN Filed Dec. l5, 1946 A TTOHNEY 2, @o2 @Z4/y0; 20

CALUTRON Lloyd P. Hunter, Oak Ridge, Tenn., assigner to the United States of America as represented by the United States Atomic Energy Commission Application December 13, 1946, Serial No. 715,953

7 Claims. (Cl. 250-41.9)

The present invention relates to an isotope separator of the electromagnetic type.

Described in general terms, this separator comprises an evacuated tank or vessel, located in a strong, substantially uniform magnetic field, having electromagnetic isotope separating means therein. The isotope separating means comprises an ion transmitter and receiver located in spaced relation along the magnetic field. The ion transmitter comprises an ion source, in which the material whose isotopes are to be separated is ionized, and accelerating and decelerating electrodes which withdraw charged ions and project them in a direction transverse, but not perpendicular to, the magnetic field. In accordance with well understood principles, this causes the ions to follow helical paths, and by special design of the electrode means, the ions may be caused to substantially focus in a zone spaced along the magnetic iield from the source. More particularly, the ion transmitter may be located centrally in the tank, and arranged to project a plurality of beams generally radially of the source, but having a slight inclination with respect to a perpendicular to the magnetic field. After substantially 360 of rotation, the ions are focused along a line generally parallel to the magnetic field, and ions of different mass, are focused in zones spaced along this line. The ion receiver referred to is located to receive, neutralize and retain one or more of the isotopes which it is desired to collect.

Where for example, the separation is to be effected between U235 and U233, the path followed by the heavier U238 ions will have a larger radius than the lighter U235 ions. It will therefore be possible to provide so-calied scraping elements along the tank wall to intercept and collect the U238 ions. The U235 ions will continue their rotation and will become substantially focused in a zone spaced along the magnetic field from the ion transmitter. Likewise in the separation of isotopes of other elements the isotopes of greater mass will be intercepted by the scraping elements and thus in the separation of lithium the isotope Li7 would be removed from the beam and lui6 collected.

Ions of less mass will complete substantially 360 of rotation in their separate helical paths at points spaced along the magnetic field from the collector, the spacing being a function of their mass. Actually these ions will be intercepted by the transmitter or other structure, but in no case will their paths reach the receiver. It will thus be possible to effect collection of the desired isotope without interference from undesired isotopes, and it will be apparent that large scale separation may be obtained, since the source may in effect project radially through some 360.

As a practical matter, since the ion transmitter is in effect a generally cylindrical body, actual reception of the desired isotope will be at a point spaced along the magnetic field from the ion transmitter, and additionally spaced circumferentially around the generally cylindrical transmitter-receiver body by a predetermined amount. However, since the transmitter transmits a great plurality of beams, the collector may be an annular body adapted 2,712,079 Patented .lune 28, 1955 to receive ions throughout its complete extent, and its selectivity depends solely on the correlation between the spacing along the magnetic field from the transmitter, and the desired focusing of the beam of ions thereon.

By properly designing the beam transmitter so that focusing in the Z dimension is also obtained, the receiver element can be relatively small in its dimension extending in the direction of the magnetic field.

With the foregoing general remarks in mind, it is an object of the present invention to effect separation of isotopes by projecting ions in helical paths through a magnetic field, whereby ions of different masses will be focused in zones spaced along the magnetic eld.

More specifically, it is an object of the present invention to provide an electromagnetic ion separator which comprises an ion beam projector arranged to transmit ion beams generally radially from a common source, through a magnetic field, and having a component parallel to said field, whereby said ions follow helical paths of radii dependent on their mass.

It is a feature of' the present invention to provide an ion transmitter centrally in an evacuated vessel effective to transmit a plurality of ion beams generally radially therefrom but having a component parallel to a magnetic field through the tank, whereby ions of different mass follow helices of different radii, in combination with means effective to intercept heavier ions after substantially 180 of rotation.

Other objects will become apparent as the description proceeds, especially when taken in conjunction with the appended drawings, in which:

Figure l is a more or less diagrammatic vertical section through an ion separator,

Fig. 2 an enlarged vertical section through the ion transmitter thereof, and

Fig. 3 is a diagrammatic view illustrating the specific design of electrodes in the ion transmitter.

Referring first to Fig. 1, I have shown a tank 10, which is connected to suitable pumping apparatus (not shown) effective to reduce the pressure in the tank to a figure on the order of 10-4 to 10-5 mm. of Hg. The electromagnetic separating mechanism indicated generally at 11 is substantially cylindrical in shape and comprises an ion beam transmitter 12 and an ion beam receiver 13. The ion beam transmitter 12 is adapted to transmit a plurality of ion beams generally radially from the source, but having a component parallel to the magnetic field, which in this gure is parallel to the axis of the generally cylindrical transmitter-receiver structure. The magnetic field may be established by an electromagnet including pole pieces 16 and windings 17, as shown in part in Fig. l.

A plurality of so-called Scrapers 14 are secured to the interior of the tank wall and Where the lighter ion or isotope is to be collected the radius of the helix of the heavier, undesired ions is adjusted by adjusting the accelerating voltage such that these ions strike the Scrapers 14.

The receiver 13 is generally annular in form and is effective throughout its entire periphery to receive, neutralize, and retain ions falling thereon. It will be apparent from elementary considerations that ions of lighter mass will complete substantially a 360 movement along their particular helical path at a point less remote in a direction parallel to the magnetic field than heavier ions. It is accordingly possible to effect selective collection of a desired isotope by positioning the receiver 13 at a predetermined distance from the transmitter l2.

Referring now to Fig. 2, I have indicated the construction of the combined transmitter-receiver unit l1 in some detail. In this figure there is shown a charge bottle 20 having a vertically extending manifold tube 2l having a plurality of perforations in its upper end through which vaporized charge material may pass. Surrounding and enclosing the upper end of the tube 21 is a frustoconical element 22, having a closed upper end, a plurality of slits 23 formed by slit defining electrode elements I and defining with the tube 21 a generally annular ionization chamber 24.

The ionizing chamber 24 is closed at its lower end by ring 25 having openings therein for the passage of electrons into the interior of the ionizing chamber 2d. Electrons for the ionization of vaporized charge material present in the ionizing chamber are supplied from a thermally emissive cathode 26 to which are connected cathode leads 27.

Tube 21 and element 22 are supported from an insulator 28, which in turn is mounted inl sealed relation on a mounting' plate 29 which is detachably secured to a Wall of the tank 10, as, for example, the bottom wall 30 thereof. Bottom wall 30 has an opening 4S therein through which the transmitter-receiver assembly may be inserted.

A generally cylindrical accelerating electrode structure 31 surrounds the frusto-conical'element 22. The electrode structure 31 has a plurality of slits formed by electrodes G and indicated at 32 which are in registry with the slits 23 formed in the element 22. Since the accelerating electrode structure is to be carried at a different electric potential from the other associated structure, it is mounted between insulator 33 and insulating ring 34. insulating ring 34 extends between the mounting plate 29 and an annular iiange 35 formed at the bottom of accelerating electrode structure 3l. Insulator 33 is secured to a sealing plate 36, which is sealingly engaged with the inner 43 Vformed by decelerating electrodes C which are in registry with the siits 23 formed in element 22 and slits 32 formed in the accelerating electrode structure 31. The body 40 is supported between sealing plate 36, and an inwardly extending annular flange 47 formed on a sup porting cage 45. The cage 45 extends between mounting plate 29 and sealing plate 36, and is formed with a plurality of slits 46 whichare in registry'with the slits 43, 32 and 23, all previously described.

It will benoted thatsealing plate 36 is of a size to be admitted through the opening 48, and, as a result, the

entire transmitter-receiver'unit may be inserted and withdrawn through this opening. It will further be observed that the body 40 is in electrical conducting relation with the plates 29 and 36 and hence with the Walls of the tank or vessel 10. This fixes the electrical potential at which the other elements are carried, since a definite difference in potential between the electrodes andthe ion source structure is required to cause the ions of a certain mass to complete 'substantially one turn in a helical path at a definite position within thetank.

In practice the element 22, which constitutes a portion of the ion source and surrounds the annular space 24 previously defined as an ionizing chamber, and particularly the electrodes l thereof is carried at a relatively high positive potential. The accelerating electrode structure, including electrodes G, is maintained at a negative potential relative to electrodes I, and the receiver is grounded. As a result positive ions of the rnaterial whose isotopes are to be separated are Withdrawn from the ionizing chamber 24, by the electric field set up between the electrodesv I 'and the relatively negative accelerating electrodes G. These ions are then slowed down and have their direction changed as will be later described in detail by the decelerating' electrodes C,

' which are at ground potential but relatively'positive with respect to electrodes G. ions are thus transmitted out into the tank in a direction generally transverse to the magnetic field, but having a slight vertical component, as will later be described. As a result of the motion of the charged particles in a magnetic field, they will be caused to follow helical paths, which will result in a predetermined vertical rise in a direction parallel to the magnetic field, depending on the length of arc each describes to complete substantially one turn of the helix. Thus each particle would, if not otherwise interrupted, return to a point spaced along the magnetic field directly above the point of its emission into the magnetic eld and the spacing of ions of different mass along a line parallel to the magnetic field will be a function of their mass.

in order to effect collection of a desired isotope, the ion transmitter is constructed and arranged to project ions in a converging beam, so that the ions which are to be coilected wiil be substantially focused at some point above the ion transmitter. In this connection, reference is now made to the diagrammatic showing of Fig.

,- 3. In this figure for convenience it is'assumed that the ion transmitter-receiver unit is positioned with its axis vertical, in a magnetic field which also extends vertically as indicated by the arrow 50.

As previously stated the element 22 is a frustum of a cone, having its larger diameter at the bottom. The adjacent edges of the accelerating electrodes G which detine the slits 32 therebetween extend parallel to the corresponding edges of the electrodes J. The deviation of these edges from vertical is indicated in Fig. 3 as the angle 0. Accordingly ions accelerated across the gap between the electrodes l and G are given a corresponding upward component, also indicated by the angle 0. In order to effect substantial focusing of the ions, the accelerating electrodes G are downwardly tapering and of varying thickness. More specifically, the exit surface of these elements is curved at a predetermined radius, the center of curvature being in a plane at the top of'the electrode structure as clearly indicated in this figure. The electric field between the electrodes G and C acts to decelerate the ions, and also to change their direction in a predetermined manner so that ions of the desired mass are substantially focused in an annular zone lying above the transmitting structure.

While the exact design of the ion transmitting structure, and more particularly the design of the accelerating and decelerating electrodes and the angle of the frustum of the cone of the element 22 is a matter of straightforward mathematics, the following typical arrangement is described in detail as an example. Assume dimensions as given below:

Lengths of slits 23 inches-- 8.00 Radius of U235 ion paths do 12.00 Diameter of tube 2l do 0.75 Average I. D. element 22 do y1.00 Average O. D. element 22 do 1.25 Width slits 23 d0 0.25 Number of slits 8 Average I. D. structure 31 inches 2.25 Average O. D. structure 31 do 3.75 Average I. D structure 41 do 4.50 Average O. D. structure 41 do 5.00

Since the electron beam is introduced from one end f the ionizing chamber 24, and since the vapor is led into this chamber from the central perforated tube 2l, this arrangement might easily give rise to a slightly nonuniform supply of ionized particles in the ionizing chamber 24, in which case it would be advantageous to vary the distance of the I slit opening from the tube 2l along its length. Such a frusto-conical arrangement Vof the element 22 lends itself admirably to the start of the Z focusing required to bring the desired isotope ions to the receiver. In the specific example being described, the J slit cone may taper 0.25 on the diameter in 8" of length. if there were no other detiection of ions in the I-G-C system, each ion of U235 would rise (l/8/8)75 or 1.17 in making a substantially complete turn in its helical path the length of which is assumed to be 75. This locates the receiver annulus 1.17 above the upper end of the .T-G-C system. It is then necessary to calculate the distortion in the G-C gap required at the other end of the J-G-C system to bring ions from that end into the receiver. Simple calculation will show that in the retarding field of the G-C gap, [3, the angle of deflection of an ion entering the G-C gap at an angle 6 equals where G and I are the G and l voltage magnitudes. This angle added to the angle of inclination of the I slits gives the angle of inclination in an upward sense of the ions. In order to reach the receiver, the total angle must be or 0.122 radians at the bottom of the I--G-C system. If a G voltage of 16 kv. and a I voltage of 8 kv. is employed, angle 6 (which is the inclination from horizontal at the normal to the G-C gap) must equal (Lw or 0.145 radians 24 fir-1 where 0.016 is 0 in radians which, for focusing the ions along the entire length of the slits of the I-G-C system, requires a radius of curvature of the G-C gap of which means a difference in thickness of G (measured radially of the transmitter-receiver unit) of of the horizontal component of the velocity of the ions emerging from the top of the slit system. This requires a radius of curvature of the vanes or Scrapers 14 of 32 about a center located on a radial line passing through the top of each scraping vane.

Best utilization of tank space requires an end mount for the transmitter-receiver structure, and this in turn lends itself to utilization of a solenoid type magnetgfor supplying the magnetic field. Under the voltagereonditions given above, the field required is 6,600 'gailssg land calculation of the necessary turns and current requirements may readily be made.

It will be appreciated that the specific electromagnetic ion separator, and particularly the example for which dimensions and voltages have been assigned, has been described in great detail merely to facilitate the use by those skilled in the art of the present invention, the scope of which is indicated by the appended claims.

What is claimed is:

l. Apparatus for separating isotopes of elements cornprising an evacuated vessel, means for establishing a substantially uniform magnetic field therein, an ion transmitter including an ion source and ion accelerating means for projecting a plurality of ion beams in a generally radial direction from a central position in said tank, ion focusing means including electrodes disposed adjacent said ion accelerating means at an angle to said magnetic field for constraining accelerated ions to follow directions making equal acute angles with a plane perpendicular to the magnetic field, whereby ions of different mass follow different helical paths, and a receiver aligned with said ion transmitter along said magnetic field for receiving and collecting ions of a desired mass focused thereat by said focusing means.

2. An improved electromagnetic mass separator disposed in a magnetic field and comprising a substantially cylindrical ion source having its axis aligned parallel to said magnetic field, a set of ion accelerating electrodes disposed concentrically about said ion source and expelling ions radially therefrom over substantially the entire length thereof, an ion receiver axially aligned with said ion source and displaced from one end thereof along said eld, and a set of focusing electrodes disposed concentrically about said accelerating electrodes and aligned at an angle therewith along said field for imparting to ions from said source a velocity component parallel to said magnetic field whereby ions of a predetermined mass described helixes in said magnetic field and impinge upon said receiver.

3. An improved electromagnetic mass separator disposed in a magnetic field and comprising, a cylindrical ion source having its axis parallel to the enveloping magnetic field at a distance from the edges thereof and producing ions over substantially the whole cylindrical surface thereof, ion accelerating means disposed about said ion source and accelerating ions substantially radially from said source, a receiver axially aligned with said source and displaced therefrom in the direction of said magnetic field, and ion focusing means including a plurality of electrodes disposed outwardly of said ion accelerating means, said electrodes being curved throughout their length and disposed closest said ion source at the end thereof furthest from said receiver and thereby imparting to ions from said ions source different velocities in the direction of said magnetic iield depending upon their displacement from said receiver whereby substantially all ions of a predetermined mass expelled from said source are focused at said receiver.

4. An improved electromagnetic mass separator disposed in a magnetic field and comprising, a source of gas to be ionized, a perforated tube carrying said gas, arc means about said tube for ionizing gas emitted therefrom, a rst cylinder about said tube having longitudinal slots therein, said tube and cylinder being aligned parallel to said magnetic field, a second cylinder disposed about said first cylinder and tube and having longitudinal slots therein facing the slots in said first cylinder, said second cylinder having a longitudinally curved outer surface to provide a varying wall thickness thereof and having impressed thereon a potential relative to said first cylinder to accelerate ions radially from said tube substantially transverse to said magnetic field, an ion receiver axially aligned with said tube and displaced along the magnetic field therefrom at the end of said second cylinder having the greatest wall thickness, and a plurality of electrodes at a different potential than said second cylinder having the same longitudinal curvature as said second cylinder and disposed thereabout parallel to the outer surface thereof, whereby radially accelerated ions have imparted thereto a velocity component parallel to the magnetic field of a magnitude dependent upon their initial displacement from said receiver.

5. A method of separating isotopes comprising continuously ionizing a column of gas, accelerating ions radially from said gas column over the entire length thereof, subjecting said ions to a magnetic field directed parallel to said gas column thereabout whereby said ions travel curved trajectories of a radius depending upon the ionic mass, imparting to said radially accelerated ions a velocity componentl parallel to said magnetic field and varying in magnitude from a maximum at one end of said gas column to a minimum at the other end whereby said ion trajectories are constrained into helixes which after one revolution intersect a common plane along said magnetic tield from said-gas columr, and collecting ions of desired'mass at said common plane.

6. An improved calutron comprising an evacuated envelope, means establishing a magnetic iield through said envelope, an elongated ion source disposed Within said envelope in alignment with the lines of force of said magnetic eld, ion accelerating means including a curved electrode having an increasing curvature along said magnetic field, and an ion receiver aligned with said ion source along said magnetic r'ield and disposedadjacent the end of said ion accelerating electrode having the least degree of curvature whereby ions accelerated from said ion source are focused at said receiver.

7. `An improved calutron comprising an evacuated tank,

means establishing a magnetic tield having flux-lines pass` ing through said tank, an ion receiver disposed within said tank, an elongated ion source disposed within said tank in alignment with said ion receiver along said linx lines, ion accelerating means disposed adjacent said ion source for attracting ions from said source over the length thereof, and ion focusing means including electrodes disposed adjacent said ion accelerating means at an angle to said ilux lines and directed toward said ion source at the end thereof away from said ion receiver whereby ions erated from said source receive a predetermined velocity component parallel to said magnetic field and are focused at said ion receiver.

References Cited in the iile of this patent UNTED STATES PATENTS 

1. APPARATUS FOR SEPARATING ISOTOPES OF ELEMENTS COMPRISING AN EVACUATED VESSEL, MEANS FOR ESTABLISHING A SUBSTANTIALLY UNIFORM MAGNETIC FIELD THERIN, AN ION TRANSMITTER INCLUDING AN ION SOURCE AND ION ACCELERATING MEANS FOR PROJECTING A PLURALITY OF ION BEAMS IN A GENERALLY RADICAL DIRECTION FROM A CENTRAL POSITION IN SAID TANK, ION FOCUSING MEANS INCLUDING ELECTRODES DISPOSED SAID ION ACCELERATING MEANS AT AN ANGLE TO SAID MAGNETIC FIELD FOR CONSTRAINING ACCELERATED IONS TO FOLLOW DIRECTIONS MAKING EQUAL ACUTE ANGLES WITH A PLANE PERPENDICULAR TO THE MAGNETIC FIELD, WHEREBY IONS OF DIFFERENT MASS FOLLOW DIFFERENT HELICAL PATHS, AND A RECEIVER ALIGNED WITH SAID ION TRANSMITTER ALONG SAID MAGNETIC FIELD FOR RECEIVING AND COLLECTING IONS OF A DESIRED MASS FOCUSED THEREAT BY SAID FOCUSING MEANS. 